Wyeth-14643 (Wy), a peroxisome proliferator, is known to induce the expression of genes involved in peroxisomal fatty acid metabolism as well as DNA synthesis in the liver. Present work was initiated to further characterize the respective roles of hepatocytes and NPC in the mechanisms of Wy-induced carcinogenicity. Four month-old male B6C3F1 mice were treated with 200 or 100 mg Wy/kg body weight by oral gavage for 4 or 12 h, respectively. Following a two-step collagenase perfusion, hepatocytes were purified by Percoll gradient centrifugation and NPC were enriched by Nycodenz gradient centrifugation and filtration through 13-?m mesh size filter. RNA was isolated from both cell fractions and gene expression was measured by reverse transcriptase polymerase chain reaction. Expression of genes, such as CYP 4A1, the liver fatty acid binding protein (LFABP), and acyl CoA oxidase were significantly induced in hepatocytes as early as 4 hr after dosing. A similar but weaker pattern was observed in the NPC fraction and was attributed to trace contamination of NPC with hepatocytes. The constitutive COX 1 enzyme was strongly expressed in NPC but not in hepatocytes and was not induced by Wy. Preliminary results also indicated that COX 2 mRNA was not detectable in NPC obtained from control or Wy-treated mice. These results suggest that the effect of NPC on Wy-induced DNA synthesis in hepatocytes may be mediated by fatty acid metabolites formed via COX enzymes. These metabolites may undergo secondary metabolism by peroxisomal fatty acid metabolizing enzymes in hepatocytes leading to the formation of mitogenic metabolites and increased DNA synthesis. Additional experiments are in progress to confirm these findings and further characterize the respective role of these two cell types in Wy-induced liver tumors - Hepatocytes nonparenchymal cells Hepatocarcinogens peroxisome proliferators PPARa